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lived adults, but reproduction is often reduced or eliminated by cold spring and summer water temperatures and other effects of regulation. In the regulated reach of the Green River downstream from Flaming Gorge Dam, native fishes are affected both by expanding populations of non-natives fishes and by altered flows and thermal regimes. Flow and temperature regimes in the Green River have recently been re- regulated at Flaming Gorge Dam for the benefit of native fishes downstream (Muth et al. 2000, Record of Decision, U. S. Bureau of Reclamation, 2006). Protocols used for river restoration embraced re-establishment of natural physical processes in streams with hypothesized benefits for native biota, including fishes (Stanford et al. 1996, Poff et al. 1997). Re-establishment of annual flow maxima to maintain channel geomorphology and flood plain connectedness, reduction of base flow fluctuations to enhance stability and food web functioning of low velocity nearshore areas, and restoration of more natural seasonal temperature patterns are examples of key processes that may facilitate recovery of native biota (Stanford et al. 1996, Poff et al. 1997). However, re-regulated flow and thermal regimes may also influence non-native fish populations in affected reaches and may result in uncertainty about whether such management actions provide a net positive benefit for native fishes (Propst and Gido 2004, Bestgen et al. 2006). For example, it is difficult to isolate effects of flow or temperature regimes on native fishes when distribution and abundance of invasive species are expanding, perhaps through interactions with variable environmental conditions (Bestgen et al. 2006). Thus, a main challenge of testing river restoration hypotheses is linking population measurements such as fish abundance to a driving variable or set of flow or temperature variables with reasonable certainty, while also considering the potentially large effect that non-native predaceous fish populations may have on native fishes. ~'he goal of this study is to report on non-native fish removal efforts in the Green River in Lodore and Whirlpool Canyon. We examine trends in distribution and abundance of selected non-native fishes, from 2002-2004 (Bestgen et al. 2006) and 2005-2006 when flows were relatively low and water temperatures in summer were warm, and compare those trends with abundance levels estimated from 1994-1996, a period prior to introduction or expansion of 2